The ratio of the main constituent elements of Q345 steel is basically the same as that of 16Mn steel. The difference is the addition of Ti, Nb, and V trace alloying elements. A small amount of Ti, V, and Nb alloy elements can refine the grains, improve the toughness of the steel, and greatly improve the comprehensive mechanical properties of the steel. Because of this, the thickness of the steel plate can be made larger. Therefore, the comprehensive mechanical properties of Q345 steel should be better than 16Mn steel, especially its low temperature performance is not available in 16Mn steel. The allowable stress of Q345 steel is slightly higher than that of 16Mn steel.
Tips: In case ASTM A53 Grade B in ERW (electric resistance welded) pipe, the weld seam shall be done the heat treatment with a minimum 1000°F [540°C]. In this way the no untempered martensite remains.
In case ASTM A53 B pipe in cold expanded, then expansion should not exceed 1.5% of the required OD.